learning challenges describe how a phospholipids is different to a triglyceride (d) identify the...
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Learning Challenges
Describe how a phospholipids is different to a triglyceride (D) Identify the relative parts on a diagram of the plasma membrane (D)Describe the arrangement of phospholipids, proteins & carbohydrates using the fluid-mosaic model ( C)Describe and explain the role of carrier proteins and protein channels in facilitated diffusion. (C>)
• YOU WILL HAVE A RESIT OF YOUR CELLS AND MITOSIS TEST NEXT WEEK ON WEDNESDAY OR THURSDAY!!!
I WANT YOUR COMLETED LAB BOOKS ON WEDNESDAY NEXT WEEK!!!!!
Chapter 2.3
Objectives of unit:
• Understand the structure and properties of the plasma membrane
• Investigate the properties of plasma membranes practically
• Explain passive transport mechanisms of diffusion and facilitative diffusion, including the role of transporter and carrier proteins
• Define the process of osmosis
• Explain the process of active transport and the role of proteins and ATP
• Explain the processes of endocytosis and exocytosis
• Describe the properties of gas exchange surfaces in living organisms
• Explain how the structure of the mammalian lung is adapted for rapid gaseous exchange
Learning Challenges
Describe how a phospholipids is different to a triglyceride (D) Identify the relative parts on a diagram of the plasma membrane (D)Describe the arrangement of phospholipids, proteins & carbohydrates using the fluid-mosaic model ( C)Describe and explain the role of carrier proteins and protein channels in facilitated diffusion. (C>)
Cells have many membranes:
plasma membrane
tonoplast
outer mitochondrial membrane
inner mitochondrial membrane
outer chloroplast membrane
nuclear envelope
Learning Challenges
Describe how a phospholipids is different to a triglyceride (D) Identify the relative parts on a diagram of the plasma membrane (D)Describe the arrangement of phospholipids, proteins & carbohydrates using the fluid-mosaic model ( C)Describe and explain the role of carrier proteins and protein channels in facilitated diffusion. (C>)
Membranes are flexible and able to break and fuse easily
Neutrophil engulfing anthrax bacteria.
Cover credit: Micrograph by Volker Brinkmann, PLoS Pathogens Vol. 1(3) Nov. 2005.
5 μm
https://www.youtube.com/watch?v=Z_mXDvZQ6dU
Learning Challenges
Describe how a phospholipids is different to a triglyceride (D) Identify the relative parts on a diagram of the plasma membrane (D)Describe the arrangement of phospholipids, proteins & carbohydrates using the fluid-mosaic model ( C)Describe and explain the role of carrier proteins and protein channels in facilitated diffusion. (C>)
Membranes allow cellular compartments to have different
conditions
pH 4.8Contains digestive enzymes, optimum pH 4.5 - 4.8
pH 7.2
lysosome
cytosol
Membrane acts as a barrier
Learning Challenges
Describe how a phospholipids is different to a triglyceride (D) Identify the relative parts on a diagram of the plasma membrane (D)Describe the arrangement of phospholipids, proteins & carbohydrates using the fluid-mosaic model ( C)Describe and explain the role of carrier proteins and protein channels in facilitated diffusion. (C>)
Membranes are mainly made of phospholipids
phosphate group
glycerol
fatty acid
phosphoester bond
ester bond
hydrophilichead
hydrophobictail
Learning Challenges
Describe how a phospholipids is different to a triglyceride (D) Identify the relative parts on a diagram of the plasma membrane (D)Describe the arrangement of phospholipids, proteins & carbohydrates using the fluid-mosaic model ( C)Describe and explain the role of carrier proteins and protein channels in facilitated diffusion. (C>)
Phospholipid
Learning Challenges
Describe how a phospholipids is different to a triglyceride (D) Identify the relative parts on a diagram of the plasma membrane (D)Describe the arrangement of phospholipids, proteins & carbohydrates using the fluid-mosaic model ( C)Describe and explain the role of carrier proteins and protein channels in facilitated diffusion. (C>)
Phospholipid
The polar hydrophilic heads are water soluble and the hydrophobic heads are water insoluble
aqueous solution
Hydrophilic (water-loving) head
Hydrophobic (water-hating) tail
Phospholipids form micelles when submerged in water
air
Learning Challenges
Describe how a phospholipids is different to a triglyceride (D) Identify the relative parts on a diagram of the plasma membrane (D)Describe the arrangement of phospholipids, proteins & carbohydrates using the fluid-mosaic model ( C)Describe and explain the role of carrier proteins and protein channels in facilitated diffusion. (C>)
In 1925 Gorter and Grendel proposed that the unit membrane is formed from a phospholipid
bilayer
Extracellular space (aqueous)
Cytosoplasm (aqueous)
phospholipid bilayer
Phosphate heads face aqueous solution
Hydrophobic tails face inwards
Question: Explain why phospholipids form a bilayer in plasma membranes (4).• Phospholipids have a polar phosphate group which are hydrophilic and
will face the aqueous solutions• The fatty acid tails are non-polar and will move away from an aqueous
environment• As both tissue fluid and cytoplasm is aqueous • phospholipids form two layers with the hydrophobic tails facing inward • and phosphate groups outwards interacting with the aqueous
environment
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Learning Challenges
Describe how a phospholipids is different to a triglyceride (D) Identify the relative parts on a diagram of the plasma membrane (D)Describe the arrangement of phospholipids, proteins & carbohydrates using the fluid-mosaic model ( C)Describe and explain the role of carrier proteins and protein channels in facilitated diffusion. (C>)
Initial studies showed that the plasma membrane had layers:
Scientists also found that protein were present in membranes so Davson-Danielli proposed in 1935 the following model for membrane structure:
Protein Phospholipid bilayer
Learning Challenges
Describe how a phospholipids is different to a triglyceride (D) Identify the relative parts on a diagram of the plasma membrane (D)Describe the arrangement of phospholipids, proteins & carbohydrates using the fluid-mosaic model ( C)Describe and explain the role of carrier proteins and protein channels in facilitated diffusion. (C>)
The development and use of electron microscopes showed that the Davson-Danielli
model was incorrect
In the early 1970s Singer and Nicholson used techniques such as freeze-etching to confirm the lipid bilayer.
They also showed that the proteins were distributed throughout the protein in a mosaic pattern.
In addition they found that the membrane was fluid and had considerable sideways movement of molecules within it.
Hence they proposed the Fluid-Mosaic Model for Plasma Membrane Structure.
Learning Challenges
Describe how a phospholipids is different to a triglyceride (D) Identify the relative parts on a diagram of the plasma membrane (D)Describe the arrangement of phospholipids, proteins & carbohydrates using the fluid-mosaic model ( C)Describe and explain the role of carrier proteins and protein channels in facilitated diffusion. (C>)
Activity:
• Read pages 100 – 103 of your textbook
• Answer questions 1 – 3 on page 103
The fluid mosaic model of the plasma membrane:
The proteins can move freely through the lipid bilayer.
The ease with which they do this is dependent on the number of phospholipids with unsaturated fatty acids in the phospholipids.
Learning Challenges
Describe how a phospholipids is different to a triglyceride (D) Identify the relative parts on a diagram of the plasma membrane (D)Describe the arrangement of phospholipids, proteins & carbohydrates using the fluid-mosaic model ( C)Describe and explain the role of carrier proteins and protein channels in facilitated diffusion. (C>)
Fat-soluble organic molecules can diffuse through the bilayer but polar molecules require proteins
Extracellular space
Cytosoplasm (aqueous)
Fat-soluble molecules Polar molecules
hydrophilic pore
diffusionfacilitated diffusion
Question 4: How can polar and non-polar molecules pass through the membrane (2).
•Polar molecules require proteins to enable them to pass through the membrane
•Non-polar molecules can diffuse directly through the phospholipid bilayer
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The membrane contains many types of protein:
glycoprotein
carbohydrate chain
integral proteinperipheral protein
carrier protein
Glycocalyx: For cell recognition so cells group together to form tissues
Receptor: for recognition by hormones
Enzyme or signalling protein hydrophilic channel
Question: Label the diagram (11marks)
1
2 10
3
4
5 6
8
9
11
Note: label the proteins based on location or structure, e.g. you do not need to identify receptors and enzymes.
1) carbohydrate; 2) glycoprotein; 3)integral protein; 4) peripheral protein; 5) carrier protein 6) hydrophilic channel; 7) phosphate group; 8) fatty acid; 9) phospholipid; 10) glycocalyx; 11) phospholipid bilayer click to cover answers
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7
Question: Explain why the model for membrane structure is known as the fluid mosaic model (3).
• The phospholipid molecules can move freely laterally and makes the membrane fluid.
• The proteins are distributed throughout the membrane un evenly and in a mosaic pattern.
• The agreed structure is based upon experimental and chemical evidence and so is classed as a model.
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Question: Describe the structure and function of the glycocalyx (3)
• Consists of glycoproteins• Which are proteins with added carbohydrate chains• Used for cell recognition/receptors• Click here to hide answersClick to reveal answers
There are different types of carrier proteins in the membrane:
ATP
Channel proteinGated-channel proteinCarrier protein(passive)
Carrier protein(active)
Membrane bound proteins allow chemical processes to occur on membranes in a sequential manner:
ATP synthase
Enzyme and transporter proteins involved in aerobic respiration in the inner mitochondrial membrane
membrane
Q IIIIII
IV
Cyt c
proteins
Question: Other than as carrier proteins state two functions of membrane bound proteins (2).
• Receptors• Enzymes• Structural (attached to microtubules)• Click here to hide answers
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Practical Activity: Factors affecting membrane permeability
• What experiment would you have done to see this?
Permeability Three factors affect the permeability of a cell membrane:
heat ethanol pH
Try and explain how these factors affect the membrane, by referring to the fluid mosaic model.
A temperature exceeding the optimum and pH levels beyond the normal range can denature the membrane’s proteins. Ethanol dissolves the lipid components of the membrane. This all makes the membrane far more permeable acting as if it is full of holes.
Help
Membrane PermeabilityPlasma membranes are semi-permeable – this means that some substances can pass through and others cannot. What is it that determines what substances pass through? The substance has to be very soluble in the oily phospholipid bilayer. Steroid hormones, oxygen and carbon dioxide are examples of such molecules.
steroid hormone
oxygencarbon dioxide
Glucose
Protein
Lipid
SOLUBLE
INSOLUBLE
Absorbance %
Experiment
5°C
0.04
Click the arrows to adjust the temperature
Experiment
22.5°C
Absorption %
0.075
Experiment
40°C
Absorption %
0.12
Experiment
52°C
Absorption %
0.25
Experiment
60°C
Absorption %
0.64
Experiment
68°C
Absorption %
0.70
Results
Results Table GraphTemperature
(°c)Absorption/ %
5 0.04
22.5 (Room Temperature)
0.075
40 0.12
52 0.25
60 0.64
68 0.7
Graph to show change in membrane permeability with an increase in temperature
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 10 20 30 40 50 60 70 80
Temperature/°CA
bso
rpti
on
/ %
4.6
Conclusion
The increase in temperature causes the proteins in the membrane to denature and so its permeability increases, causing substances (purple dye in this case) to escape.
Question 3: Describe an experiment by which you could test to see whether alcohol concentration affected membrane permeability (5).
• Same volume discs of beetroot• Same volume of alcohol• Same temperature• Same time in alcohol• Range of alcohol concentrations• Use colourimeter to read amount of pigment in solution• Graph of colour intensity (% absorbance etc.) over alcohol concentration
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Learning Challenges
Describe how a phospholipids is different to a triglyceride (D) Identify the relative parts on a diagram of the plasma membrane (D)Describe the arrangement of phospholipids, proteins & carbohydrates using the fluid-mosaic model ( C)Describe and explain the role of carrier proteins and protein channels in facilitated diffusion. (C>)
Summary• The unit membrane consists of a phospholipid bilayer
• Phospholipids consist of a polar, hydrophilic phosphate head and a non-polar, hydrophobic tail consisting of fatty acid chains.
• Proteins also occur in the membrane and float freely throughout it.
• The model for membrane structure is known as the fluid mosaic model.
• Peripheral proteins occur on the inner or outer face of the membrane and integral proteins extend through both lipid layers.
• Membrane bound enzymes occur allowing structured metabolic pathways.
• Glycoproteins form the glycocalyx and allow cell to cell recognition.
• Receptor proteins can act as binding sites for hormones and other substances and can transmit the information to the interior of the cell.
• A variety of carrier proteins allow for the controlled movement of substance through the membrane using both passive diffusion or active transport.
• Non-polar, lipid soluble molecules diffuse through the phospholipid bilayer.
• Ionic, polar molecules require carrier proteins to enable them to pass through the membrane.
• Membrane structure loses integrity with high temperature or presence of organic solvents such as alcohol, thereby increasing permeability.